Helical Bilayer Nonbenzenoid Nanographene Bearing a [10]Helicene with Two Embedded Heptagons

The precision synthesis of helical bilayer nanographenes (NGs) with new topology is of substantial interest because of their exotic physicochemical properties. However, helical bilayer NGs bearing non-hexagonal rings remain synthetically challenging. Here we present the efficient synthesis of the first helical bilayer nonbenzenoid nanographene (HBNG1) from a tailor-made azulene-embedded precursor, which contains a novel [10]helicene backbone with two embedded heptagons. Single-crystal X-ray analysis reveals its highly twisted bilayer geometry with a record small interlayer distance of 3.2 angstrom among the reported helical bilayer NGs. Notably, the close interlayer distance between the two layers offers intramolecular through-space conjugation as revealed by in situ spectroelectrochemistry studies together with DFT simulations. Furthermore, the chiroptical properties of the P/M enantiomers of HBNG1 are also evaluated by circular dichroism and circularly polarized luminescence.

Automated summary

The synthesis of helical bilayer nanographenes with new topology has attracted great interest due to their unique physicochemical properties. In this study, the first helical bilayer nonbenzenoid nanographene (HBNG1) was successfully synthesized from a specially designed precursor. The HBNG1 not only possesses a novel [10]helicene backbone with two embedded heptagons, but also exhibits a highly twisted bilayer geometry with a record small interlayer distance of 3.2 angstrom. The close interlayer distance allows for intramolecular through-space conjugation, as evidenced by spectroelectrochemistry studies and DFT simulations. The chiroptical properties of the P/M enantiomers of HBNG1 were also evaluated using circular dichroism and circularly polarized luminescence.